In such an arrangement, the dashboard which is located in the cab below the windscreen comprises a dashboard body with a lower face carrying an inflatable airbag module. In concrete terms, this module, which comprises an enclosure for the airbag and its inflation means, is mounted facing a delimited opening in the dashboard body.
The opening, which is generally rectangular, is defined for example by one or more weakening lines constituting as applicable one or two flaps intended to open on deployment of the airbag. The mounting which constitutes a firing channel for the airbag is located below the lower face of the dashboard body to which it is fixed and the airbag module it carries is attached to the lower face of the mounting.
This mounting is thus interposed between a flat, standardized airbag module fixing surface and the lower face of the dashboard body which is curved, the form of which varies from one vehicle model to the next.
The upper face of the dashboard body is a surface with a substantially continuous curvature which may be covered with a covering typically comprising a foam and a skin, the inflatable airbag being arranged virtually invisibly at the upper face.
When an impact is detected, the airbag inflates and exerts a pressure on the inner face of the flap or flaps, thus causing the opening, against the covering which tears. This opening allows the airbag to deploy through the dashboard towards the cab to protect a vehicle occupant in the case of impact.
As the dashboard extends over a relatively large area, in particular over the entire width of the vehicle in which it is fitted, and its body is made of a relatively flexible material, its form or curvature changes significantly as the vehicle ages, in particular taking into account the substantial thermal variations resulting namely from the extensive exposure to sunlight of such a dashboard.
In practice, the shape of the module mounting becomes apparent on the upper face of the dashboard: the form of the dashboard changes while that of the mounting fixed to the dashboard does not change because the mounting is made of a more rigid material than the dashboard. In concrete terms, the shape of the module mounting becomes apparent on the upper face of the dashboard body.
One solution to solve this problem consists of producing the mounting from a material with a flexibility comparable to that of the dashboard body.
In this case the mounting deforms with the dashboard over the life of the vehicle such that, despite the deformation of this dashboard, the shape of the mounting remains invisible on the upper face of the dashboard body.
In this case however the fixing of the inflatable airbag module to the mounting is problematical as the mounting material is too flexible to allow a fixing with sufficient mechanical strength. This problem is all the greater as it can result in the detachment of the module when the airbag inflates.
In the case of detachment of the module, the airbag cannot exert sufficient pressure on the rear face of the dashboard body to allow opening of the flap, such that the airbag simply cannot deploy into the cab.